N.B. An asterisk before a word means it has its own entry in the glossary.

variations

Font variations are the TrueType *GX equivalent of Adobe's *multiple master technology.
Instead of specifying the extremes of each *design axis, a variations font has one "central" outline, with maximum positive and negative displacements specified for each point in each axis. Variations fonts with multiple axes theoretically involve less work than the equivalent multiple master, since each axis doubles the number of masters in MM fonts, but only adds two to the number of outlines in a GX variations font (1 axis=3 GX masters vs 2 MM masters; 2 axes=5 vs 4; 3 axes=7 vs 8; 4 axes=9 vs 16). But that's hardly a compelling reason to choose one over the other, since no 4-axis font has ever been released. Variations fonts require a *'gvar' table and an *'fvar' table.

Visual TrueType (VTT)

Microsoft's professional TrueType hinting tool.
A development of *TypeMan, VTT uses the *TypeMan Talk language (as well as its own visual representation) to simplify the hinting task. A Windows version is available as well as the Mac version. There's an official VTT website.